The US State Department has ordered more than half its Embassy staff and all diplomatic family members to leave Cuba because of a mysterious “specific attacks” that have caused myriad health problems to 21 diplomats.

Only those who carry out the main U.S. diplomatic and consular duties, including providing emergency assistance to American travelers in Cuba, will stay at the embassy in Havana, officials said.

The State Department issued an advisory for Americans not to visit Cuba, although no tourists or other travelers have been affected by the still-unexplained attacks, which some outside experts suspect came from an acoustic device.

The embassy, an iconic building on Havana’s waterfront, also will suspend processing U.S. visa applications.

Secretary of State Rex Tillerson said he had decided to trim staff and warn Americans in response to what he called “attacks of an unknown nature.” He emphasised that the moves were intended to ensure the health and safety of embassy personnel, not to punish Cuba.

“Until the Government of Cuba can ensure the safety of our diplomats in Cuba, our Embassy will be reduced to emergency personnel in order to minimise the number of diplomats at risk of exposure to harm,” Tillerson said.

Still, the dramatic moves were a blow to Washington’s delicate relations with Havana, which were restored in 2015, more than half a century after they were broken in the Cold War.

Over the last two years, U.S. airlines have begun direct flights to Cuba, tourism has surged and numerous travel and commerce restrictions were lifted. President Trump has reversed some changes but has broadly left the rapprochement in place.

Tillerson issued the statement in Beijing, where he is meeting Chinese officials to discuss efforts to restrain North Korea and to help set up Trump’s visit in November.

Aides said he made the decision on the flight from Washington, after considering options that included temporarily closing the embassy.

In all, 21 U.S. diplomats in Cuba have exhibited a wide range of physical symptoms, including ear complaints, hearing loss, dizziness, headache, fatigue, cognitive issues and difficulty sleeping. Several Canadian diplomats also have reported unusual physical ailments.

“Investigators have been unable to determine who is responsible or what is causing these attacks,” Tillerson said. Moreover, he said, the State Department “is unable to recommend a means to mitigate exposure.”

U.S. officials said the attacks occurred in the diplomats’ residences and in local hotels they frequent. The attacks began in mid-2016, and the most recent was in August.

The government mostly has referred to “incidents” rather than attacks in the past. But officials said Friday the U.S. now believes “specific attacks” targeted the diplomats in Cuba.

Tillerson emphasised that the U.S. is not breaking diplomatic relations with Cuba, noting that Havana “has told us it will continue to investigate these attacks and we will continue to cooperate with them in this effort.”

“We maintain diplomatic relations with Cuba, and our work in Cuba continues to be guided by the national security and foreign policy interests of the United States,” he said.

Cuba has allowed FBI agents in to help investigate the rash of health problems. And the Trump administration has stopped short of blaming Cuba for the attacks, leaving open the possibility that another country or group is responsible.

Experts have theorised that the attacks have been carried out by a machine that sends high-powered sound waves at a person, vibrating brain tissue and parts of the ear.

Russian intelligence agents have been known to use audio weapons, but the U.S. has not definitively determined who is responsible for the attacks in Cuba.

Investigators have struggled to unravel the mystery. FBI agents and other agencies have found devices in or near the homes and hotels that were affected. The wide range of symptoms, and questions of how and when people were impacted, have yet to yield clear clues.

Some diplomats reported hearing loud noises or feeling vibrations when the incidents occurred, but others heard and felt nothing yet reported symptoms later. In some cases, the effects were narrowly confined, with victims able to walk “in” and “out” of blaring noises audible in only certain rooms or parts of rooms, the AP has reported.

In a telephone briefing, a State Department official said the decision was aimed at reducing “the number of Americans who are vulnerable to exposure” from possible attacks.

“At this moment, we don’t have definitive information about the source or cause of the attacks,” said the official, who briefed reporters on condition of anonymity. (LA Times/NAN)